The woman's weight must be placed on the ball of the foot in order for her to pivot as if on a fixed pin. But she does not pivot her whole body. She only pivots her lower body from the waist down. The waist is like the swivel that joins the upper body and the lower body. Since her torso is connected to his torso in the embrace, she needs to pivot her lower body sideways to dance around him. This technique is known as “dissociation”.
An experienced woman knows that a subtle twist of her torso by the man indicates and must result in a big rotation of her lower body. The man leads her by turning her torso slightly to the direction that he wants her to move. On receiving the signal she needs to swivel her hips to let her lower body face that direction. In this twisted position she is able to walk on the side of the man while her torso is connected to his torso. The rotation of her hips does not need to be huge. In most cases a 30-45 degree rotation of the hips will enable her to walk on the side of the man. In some cases, such as gancho and back sacada, overt rotation of the hips is required.
It needs to be pointed out that dissociation is different from CBM (contra-body movement). CBM is turning the right side of the body towards a left moving leg or turning the left side of the body towards a right moving leg, but dissociation is swiveling the upper body or the lower body only. In tango we often need to turn only the upper body and keep the lower body still, or turn only the lower body and keep the upper body still. Both are the forms of dissociation. The former is not difficult to do but the latter is much harder and needs a lot of practice to master. When practicing dissociation in front of a mirror, you should let your torso face the mirror still and swivel only your lower body from the hips down. You should not cheat by turning the torso instead of swiveling the hips.
A typical figure using dissociation is the front ocho, in which the man leads her to draw an S on the floor with one leg, then draw another S on the floor with the other leg. The two S's are overlapped in the opposite directions so they look like the figure 8. To dance the front ocho, she needs to swivel her hips to one side of him and make a forward step with one leg, then swivel her hips to the other side of him and make another forward step with the other leg, and then swivel her hips back to face the man. A similar figure using this technique is the back ocho, in which she dances the ocho backward. She first swivels her hips and steps backward to one side of him with one leg, then swivels her hips and steps backward to the other side of him with the other leg. If she is able to overturn her hips, she can move forward by doing the back ocho and move backward by doing the front ocho. A third example using dissociation is the molinete, which is a combination of four steps, a forward step, a side step, a back step, a side step, in a circular motion. In all these examples the woman keeps her chest connected to the man's torso and rotates only her hips side to side. The technique suits the flexible body of the woman and highlights her femininity as she turns her hips alternately while her chest remains connected to the man.
The rotation of the hips causes her chest to roll on his chest, generating a pleasant sensation know as "gear effect". The chest is the center of her attention through which everything, including emotion, feeling, music interpretation, intention, seduction and flirtation, is expressed and exchanged. The woman should not glue her chest on the man's torso, but should let it roll as she swivels her hips. At each swivel of the hips, the weight is turned to one side of her chest. As she swivels her hips to the other side, her chest rolls along on his torso until the weight is transferred to the other side.
The rolling of the chest is caused by the rotation of the hips. She needs to make the rolling void of abruptness and bumpiness so it feels smooth, musical and comfortable, which is not easy to do and needs a lot of practice to master. A beginner who does not know how to rotate her hips often crosses one leg in front of or behind the other leg instead. Consequently, her chest sticks on his torso and does not trundle. Tango is a dance in which both partners pleasure each other with their bodies. An experienced woman knows how to use her body to please the man, just like an experienced man knows how to display her feminine beauty. (See Revealing her Beauty in Tango.) Gear effect increases the sensual pleasure of the dance - a feature of close-embrace tango that is missing in the open-embrace style. It is one of the things that make the two styles fundamentally different.